"""add previous_work_command_id columnRevision ID: 2dda2c7c7e83Revises: 430e5c7bc3aaCreate Date: 2013-07-23 17:07:43.708000"""# revision identifiers, used by Alembic.revision = '2dda2c7c7e83'down_revision = 'e8e10d94c8e'from alembic import opimport sqlalchemy as sadef upgrade():    op.add_column("TB_WORK_COMMAND", sa.Column("previous_work_command_id", sa.Integer, sa.ForeignKey("TB_WORK_COMMAND.id", name="fk_previous_wc")))def downgrade():    op.drop_constraint("fk_previous_wc", "TB_WORK_COMMAND", type_="foreignkey")    op.drop_column("TB_WORK_COMMAND", "previous_work_command_id")